Resistors and IV graphs: Electricity: Physics: GCSE (9:1)

• Ohm's Law (V = IR)


  The current flowing through a device is directly proportional to the potential difference across the it (providing the temperature remains constant)

  
• Directly proportional


  When a graph of two variables is a straight line that passes through the origin (0,0)

  
• Ohmic conductor


  A device that obeys Ohm's Law

  
• Fixed resistor

  An ohmic conductor that obeys Ohm's Law because its resistance is fixed

  
• Filament bulb

  Not an ohmic conductor because it doesn't obey Ohm's Law

  
• Diode

  Not an ohmic conductor because it doesn't obey Ohm's Law

  
• Reason why a filament bulb is not an ohmic conductor

  The filament gets hot which causes its resistance to increase
• Reason why a diode is not an ohmic conductor

  Its resistance changes depending on which direction the current flows through it
• IV (current-potential difference) graph


  a graph used to show how the current through a component varies as the potential difference across it changes

  
• What the gradient of an IV graph represents

  The resistance of a component (equal to 1/R)

  
• What a steep line on an IV graph represents

  A device with a low resistance because increasing the potential difference by a small amount causes a large increase in current

  
• What a shallow line on an IV graph represents

  A device with a high resistance because increasing the potential difference by a small amount causes a small increase in current

  
• IV graph for a fixed resistor

  A straight line which passes through the origin

  
• IV graph for a filament lamp

  A s-shaped curve which passes through the origin

  
• IV graph for a diode

  The graph a horizontal line along the x-axis until it reaches around 0.6 V, where it then becomes a straight line with a steep gradient

  
• Thermistor

  The resistance of a thermistor decreases as the temperature increases

  
• LDR (light dependent resistor)


  The resistance of an LDR decreases as light intensity increases